APOD: Dark Molecular Cloud Barnard 68 (2020 Nov 22)

[APOD Robot]

Dark Molecular Cloud Barnard 68

Explanation: Where did all the stars go? What used to be considered a hole in the sky is now known to astronomers as a dark molecular cloud. Here, a high concentration of dust and molecular gas absorb practically all the visible light emitted from background stars. The eerily dark surroundings help make the interiors of molecular clouds some of the coldest and most isolated places in the universe. One of the most notable of these dark absorption nebulae is a cloud toward the constellation Ophiuchus known as Barnard 68, pictured here. That no stars are visible in the center indicates that Barnard 68 is relatively nearby, with measurements placing it about 500 light-years away and half a light-year across. It is not known exactly how molecular clouds like Barnard 68 form, but it is known that these clouds are themselves likely places for new stars to form. In fact, Barnard 68 itself has been found likely to collapse and form a new star system. It is possible to look right through the cloud in infrared light.

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[BDanielMayfield]

... half a light-year across. It is not known exactly how molecular clouds like Barnard 68 form, but it is known that these clouds are themselves likely places for new stars to form. In fact, Barnard 68 itself has been found likely to collapse and form a new star system.

This then is proof that not all stellar systems form in groups, some stars can and do form by themselves. Interesting. Is solo system formation rare or common?

[VictorBorun]

A seat rather than a booty. 3d is from here https://arxiv.org/abs/1208.4512

[VictorBorun]

made a "drying puddle anime" https://www.facebook.com/AstronomyPictu ... _tn__=R]-R to show how Barnard 68 becomes transparent in infrared. but can't see how to post it on this forum

[vdix]

500 light year away in that direction and there are no stars in front of it? That seems unlikely.

[BDanielMayfield]

500 light year away in that direction and there are no stars in front of it? That seems unlikely.

But this cloud is very small as these objects go, being "only half a light year across." Something that small even at that distance could easily have no stars between us and it. Space is mostly empty. The average spacing between neighboring star systems around here is, what, about 5 ly or so.

[BDanielMayfield]

500 light year away in that direction and there are no stars in front of it? That seems unlikely.

But this cloud is very small as these objects go, being "only half a light year across." Something that small even at that distance could easily have no stars between us and it. Space is mostly empty. The average spacing between neighboring star systems around here is, what, about 5 ly or so.

Plus this from the linked to wikipedia article on Barnard 68:

Barnard 68 is a molecular cloud, dark absorption nebula or Bok globule, towards the southern constellation Ophiuchus and well within our own galaxy at a distance of about 400 light-years, so close that not a single star can be seen between it and the Sun.

[BDanielMayfield]

Stellar density in solar neighborhood is only 0.004 stars per cubic light year

Stellar density is the average number of stars within a unit volume. It is similar to the stellar mass density, which is the total solar masses (MSun) found within a unit volume. Typically, the volume used by astronomers to describe the stellar density is a cubic parsec (pc³).

In the solar neighborhood, this value can be determined from surveys of nearby stars, combined with estimates of the number of faint stars that may have been missed. The true stellar density near the Sun is estimated as 0.004 stars per cubic light year, or 0.14 stars pc³.

The volume of a cone with a length of 400 LY and a base of 0.25 LY is only about 26 LY³. The odds of a star being between us and an object as small as Barnard 68 is only 0.004*26 or about 0.104 to 1.

[orin stepanek]

Kinda spooky little Twerp! It's density is so amazing
that it hides all the stars behind it!

It is possible to look right through the cloud in infrared light.

I'd like to see a photo of that; (maybe I missed it!)

[Chris Peterson]

... half a light-year across. It is not known exactly how molecular clouds like Barnard 68 form, but it is known that these clouds are themselves likely places for new stars to form. In fact, Barnard 68 itself has been found likely to collapse and form a new star system.

This then is proof that not all stellar systems form in groups, some stars can and do form by themselves. Interesting. Is solo system formation rare or common?

The number of stars that form in a molecular cloud is determined by the mass of the cloud. This one is very small, at about three solar masses. But there is no suggestion that it will necessarily produce just a single star. That is enough mass to produce several stars, depending on how the material clumps as it collapses.

[E Fish]

barnard68v2_vlt_960.jpg


Kinda spooky little Twerp! It's density is so amazing
that it hides all the stars behind it!

It is possible to look right through the cloud in infrared light.

I'd like to see a photo of that; (maybe I missed it!)

The ESO has a series of images of Barnard 68 in different wavelengths. B&W but still neat to see. https://www.eso.org/public/images/eso9934b/

[VictorBorun]

made a "drying puddle anime" https://www.facebook.com/AstronomyPictu ... _tn__=R]-R to show how Barnard 68 becomes transparent in infrared. but can't see how to post it on this forum

[jiharmer@hotmail.co.uk]

Haven't we had this picture on APOD before ? Or am I just going completely bonkers ?

[De58te]

Haven't we had this picture on APOD before ? Or am I just going completely bonkers ?

2017, October 08. And the comments there said it was also from 2014, December 14.

[heehaw]

Haven't we had this picture on APOD before ? Or am I just going completely bonkers ?

2017, October 08. And the comments there said it was also from 2014, December 14.

I LOVE seeing a great APOD, such as this one, every so often!

[johnnydeep]

Stellar density in solar neighborhood is only 0.004 stars per cubic light year

Stellar density is the average number of stars within a unit volume. It is similar to the stellar mass density, which is the total solar masses (MSun) found within a unit volume. Typically, the volume used by astronomers to describe the stellar density is a cubic parsec (pc³).

In the solar neighborhood, this value can be determined from surveys of nearby stars, combined with estimates of the number of faint stars that may have been missed. The true stellar density near the Sun is estimated as 0.004 stars per cubic light year, or 0.14 stars pc³.

The volume of a cone with a length of 400 LY and a base of 0.25 LY is only about 26 LY³. The odds of a star being between us and an object as small as Barnard 68 is only 0.004*26 or about 0.104 to 1.

Thanks for that extra math! I too couldn't quite believe there were no stars between us and Barnard 68. BTW, I just double checked your local stellar density figure using numbers from http://www.atlasoftheuniverse.com/250lys.html, which says there are about 260000 stars within 250 ly, which is 6.54e7 ly ³. That amounts to almost exactly .004 stars / ly³. What a pleasant coincidence!

There Are About 260000 Stars Within 250 Light Years Of US

---

[jiharmer@hotmail.co.uk]

Haven't we had this picture on APOD before ? Or am I just going completely bonkers ?

2017, October 08. And the comments there said it was also from 2014, December 14.

I LOVE seeing a great APOD, such as this one, every so often!

Thank you. Good to know that I'm not as crazy as I thought I was !

[BDanielMayfield]

Stellar density in solar neighborhood is only 0.004 stars per cubic light year

Stellar density is the average number of stars within a unit volume. It is similar to the stellar mass density, which is the total solar masses (MSun) found within a unit volume. Typically, the volume used by astronomers to describe the stellar density is a cubic parsec (pc³).

In the solar neighborhood, this value can be determined from surveys of nearby stars, combined with estimates of the number of faint stars that may have been missed. The true stellar density near the Sun is estimated as 0.004 stars per cubic light year, or 0.14 stars pc³.

The volume of a cone with a length of 400 LY and a base of 0.25 LY is only about 26 LY³. The odds of a star being between us and an object as small as Barnard 68 is only 0.004*26 or about 0.104 to 1.

Thanks for that extra math! I too couldn't quite believe there were no stars between us and Barnard 68. BTW, I just double checked your local stellar density figure using numbers from http://www.atlasoftheuniverse.com/250lys.html, which says there are about 260000 stars within 250 ly, which is 6.54e7 ly ³. That amounts to almost exactly .004 stars / ly³. What a pleasant coincidence!

There Are About 260000 Stars Within 250 Light Years Of US

---

And I appreciate your appreciation Johnny. The source of my quotation and the figure 0.004 stars per LY was the wikipedia article Stellar Density, which I should have mentioned in my comment. I'd say that the coincidence is that both of us got our math right.

[BDanielMayfield]

In honor of all who mainly comment on what some object in an APOD looks like,

Barn[y]ard 68 resembles a cow paddy after it's been stepped in.

Perhaps it smells like a barnyard too. (All those aromatic hydrocarbons, etc.)

[orin stepanek]

barnard68v2_vlt_960.jpg


Kinda spooky little Twerp! It's density is so amazing
that it hides all the stars behind it!

It is possible to look right through the cloud in infrared light.

I'd like to see a photo of that; (maybe I missed it!)

The ESO has a series of images of Barnard 68 in different wavelengths. B&W but still neat to see. https://www.eso.org/public/images/eso9934b/

10-Q "E Fish" I like!

[orin stepanek]

Haven't we had this picture on APOD before ? Or am I just going completely bonkers ?

2017, October 08. And the comments there said it was also from 2014, December 14.

The staff deserves a day off once in a while: so yes, Sundays are repeat days!

[neufer]

In honor of all who mainly comment on what some object in an APOD looks like,

Barn[y]ard 68 resembles a cow paddy after it's been stepped in.

Perhaps it smells like a barnyard too. (All those aromatic hydrocarbons, etc.)

• A remnant of rector Poczobutt's Taurus Poniatovii

Ophiuchus holding the serpent, Serpens, as depicted in Urania's Mirror, a set of constellation cards published in London c. 1825. Above the tail of the serpent is the now-obsolete constellation Taurus Poniatovii

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<<Taurus Poniatovii (Latin for Poniatowski's bull) was a constellation created by the former rector of Vilnius University, Marcin Odlanicki Poczobutt, in 1777 to honor Stanislaus Poniatowski, king of Poland. It consisted of stars that are today considered part of Ophiuchus and Aquila. It is no longer in use. It was wedged in between Ophiuchus, Aquila and Serpens Cauda. A depiction of the constellation can be found on the wall of the Vilnius University Astronomical Observatory.

The stars were picked for the resemblance of their arrangement to the Hyades group which form the "head" of Taurus. Before the definition of Taurus Poniatovii, some of these had been part of the obsolete constellation River Tigris. The brightest of these stars is 72 Oph (3.7 magnitude) in the "horn" of Taurus Poniatovii. The "face" of Taurus Poniatovii is formed by 67 Oph (4.0), 68 Oph (4.4) and 70 Oph (4.0).[1] The five brightest stars belong to loose open cluster Collinder 359 or Melotte 186. Barn(y)ard's star is also inside the boundaries of this former constellation. Some minor stars (5th and 6th magnitude) now in Aquila formed the "rear" of Taurus Poniatovii.>>

[Jake]

Photo from November 22, 2020 is a duplicate from December 19, 2004. You guys also need an updated “I’m not a robot” question, who wants to open new tabs and go back to try and find an editor’s name? I appreciate your times new roman 1995 internet look, it’s nostalgic for sure, but come on it’s 2020.